Question: Which of the following numbers is a factor of 99? ${5,8,11,13,14}$
Solution: By definition, a factor of a number will divide evenly into that number. We can start by dividing $99$ by each of our answer choices. $99 \div 5 = 19\text{ R }4$ $99 \div 8 = 12\text{ R }3$ $99 \div 11 = 9$ $99 \div 13 = 7\text{ R }8$ $99 \div 14 = 7\text{ R }1$ The only answer choice that divides into $99$ with no remainder is $11$ $ 9$ $11$ $99$ We can check our answer by looking at the prime factorization of both numbers. Notice that the prime factors of $11$ are contained within the prime factors of $99$ $99 = 3\times3\times11 11 = 11$ Therefore the only factor of $99$ out of our choices is $11$. We can say that $99$ is divisible by $11$.